1. Field of the Invention
The present invention pertains generally to telecommunications, and particularly to a High Speed Downlink Packet Access (HSDPA) system such as that operated (for example) in a Universal Mobile Telecommunications System (UMTS) terrestrial radio access network (UTRAN).
2. Related Art and Other Considerations
The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the Global System for Mobile Communications (GSM), and is intended to provide improved mobile communication services based Wideband Code Division Multiple Access (WCDMA) access technology. As wireless Internet services have become popular, various services require higher data rates and higher capacity. Although UMTS has been designed to support multi-media wireless services, the maximum data rate is not enough to satisfy the required quality of services. In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for third generation networks and UTRAN specifically, and investigate enhanced data rate and radio capacity.
One result of the forum's work is the High Speed Downlink Packet Access (HSDPA). The HSDPA system is provides, e.g., a maximum data rate of 10 Mbps and to improve the radio capacity in the downlink. FIG. 5 illustrates a high-speed shared channel concept where multiple users 1, 2, and 3 provide data to a high speed channel (HSC) controller that functions as a high speed scheduler by multiplexing user information for transmission over the entire HS-DSCH bandwidth in time-multiplexed intervals (called transmission time intervals (TTI)). For example, during the first time interval shown in FIG. 5, user 3 transmits over the HS-DSCH and may use all of the bandwidth allotted to the HS-DSCH. During the next time interval, user 1 transmits over the HS-DSCH, the next time interval user 2 transmits, the next time interval user 1 transmits, and so forth.
HSDPA achieves higher data speeds by shifting some of the radio resource coordination and management responsibilities to the base station from the radio network controller. Those responsibilities include one or more of the following (each briefly described below): shared channel transmission, higher order modulation, link adaptation, radio channel dependent scheduling, and hybrid-ARQ with soft combining.
In shared channel transmission, radio resources, like spreading code space and transmission power in the case of CDMA-based transmission, are shared between users using time multiplexing. A high speed-downlink shared channel is one example of shared channel transmission. One significant benefit of shared channel transmission is more efficient utilization of available code resources as compared to dedicated channels. Higher data rates may also be attained using higher order modulation, which is more bandwidth efficient than lower order modulation, when channel conditions are favorable.
Radio channel conditions experienced on different communication links typically vary significantly, both in time and between different positions in the cell. In traditional CDMA systems, power control compensates for differences in variations in instantaneous radio channel conditions. With this type of power control, a larger part of the total available cell power may be allocated to communication links with bad channel conditions to ensure quality of service to all communication links. But radio resources are more efficiently utilized when allocated to communication links with good channel conditions. For services that do not require a specific data rate, such as many best effort services, rate control or adjustment can be used to ensure there is sufficient energy received per information bit for all communication links as an alternative to power control. By adjusting the channel coding rate and/or adjusting the modulation scheme, the data rate can be adjusted to compensate for variations and differences in instantaneous channel conditions.
For maximum cell throughput, radio resources may be scheduled to the communication link having the best instantaneous channel condition. Rapid channel dependent scheduling performed at the bases station allows for very high data rates at each scheduling instance and thus maximizes overall system throughput. Hybrid ARQ with soft combining increases the effective received signal-to-interference ratio for each transmission and thus increases the probability for correct decoding of retransmissions compared to conventional ARQ. Greater efficiency in ARQ increases the effective throughput over a shared channel.
With HSDPA, the physical layer becomes more complex as an additional MAC protocol is introduced: the MAC-hs. On the network side, the MAC-hs protocol is implemented in the radio base station (RBS). The MAC-hs protocol contains the retransmission protocol, link adaptation, and channel dependent scheduling. The complexity increase with HSDPA is thus mainly related to the introduction of an intelligent Layer 2 protocol in the radio base station (RBS).
HSDPA generally has an algorithm for selecting the amount of power for the HS-DSCH and a downlink control channel known as the HS-SCCH. The HS-SCCH contains information which is sent to the mobile terminals so that the mobile terminals know if they have data to receive on the HS-PDSCh channel or not.
The most straightforward power algorithm or solution is to allocate, at every transmission time interval (TTI) of the high-speed shared channel, all unused downlink cell power to the HS-SCCH and HS-DSCH channels and to keep the power constant for the high-speed shared channel throughout the TTI after allocation. But such allocation of all unused downlink cell power can be problematic, as illustrated by the situation shown in FIG. 6. FIG. 6 shows a series of transmission time intervals (TTI0 . . . ) for the high-speed downlink shared channel (HS-DSCH), as well as a series of timeslots (TS) for a normal downlink dedicated physical channel (DPCH). The downlink dedicated physical channel (DPCH) carries both the Dedicated Physical Data Channel (DPDCH) and the Dedicated Physical Control Channel (DPCCH).
For convenience, a power graph is superimposed on the series of DPCH timeslots of FIG. 6, showing the total downlink (DL) cell power, and each DPCH timeslot appears in bargraph-like depiction showing the amount of power needed for each DPCH timeslot. In particular, the power needed for each of the first two DPCH timeslots is shown as crosshatched. The remaining DL power allocated to the TTI0 of the high-speed downlink shared channel (HS-DSCH), after allocating for DPCH timeslot TS0, is shown as a dotted superposition on the DPCH timeslots. So, at the beginning of the time shown in FIG. 6, the power for the TTI0 of the high-speed downlink shared channel (HS-DSCH) is shown as the difference between the total DL cell power and the amount allocated for other channels, i.e., the DPCH. The problem is that the power for the HS-DSCH needs to be constant during its 2 millisecond TTI, while on the other hand the normal DPCH channels are power controlled (e.g., have power allotted to them) every timeslot (0.67 ms). Therefore there is a risk that after all remaining power has been allocated to the HS-DSCH, for its next timeslot the sum or all of the DPCH channels will need more power i.e. the sum of the requested power becomes larger than needed. For example, FIG. 6 illustrates that the second timeslot TS1 of the DPCH requires greater power than the first DPCH timeslot TS0. But since the ongoing TTI0 of the high-speed downlink shared channel (HS-DSCH) is still allocated the same power level as coexisted at DPCH timeslot TS0, the summed power requirements for both DPCH and high-speed downlink shared channel (HS-DSCH) exceed the total DL power capability for the cell.
As a result of a predicament such as that illustrated by way of example in FIG. 6, the radio base station (RBS) in charge of the cell has to make some connections unsatisfied by not giving them the power they need to keep the downlink quality. This will either impact the quality on ongoing DPCH connections e.g. speech or the quality of the HS-DSCH transmission, which can result in a failed transmission, which then need a re-transmission (equal to lower throughput).
What is needed, therefore, and an object herein provided, are means, methods, and techniques for effectively powering a high-speed downlink shared channel (HS-DSCH) with less likelihood of insufficiently funding power allocation for other channels.